The invention relates to a process for the production of a standard calibration and test element for the calibration and testing of reading and measuring instruments. The invention further relates to a standard calibration and test element produced by the process.
For the machine-readable identification marking of goods, particularly food articles (which are packed in a very wide variety of shapes and materials), of books and other mass-produced articles, internationally introduced codes, which are in general bar codes containing coded information on the country of origin, article numbers, price information and further data by means of different bar thicknesses, lengths, separations and the like, are becoming generally accepted to an increasing extent. In the case of codes for the identification marking of books, for example paperbacks, such data as publisher, price, title, year of publication, edition number, language and the like are coded above all.
When these codes are read by machines, for example, in so-called scanner registers, this information is decoded and printed out in clear text on the receipt and also, in many cases, simultaneously transferred to a central computer which manages all the stockkeeping. Besides the scanners which are permanently built-in to data registers, pen-like readers are also employed for decoding bar codes, in which case these pen-like readers may be connected to the data register, and also additionally to a monitor via flexible cables.
The specifications for printing the various codes propose dark stripes or bars and pale gaps; the contrast specifications, however, are only valid for the wavelength range in which the light source employed for the decoding works. The scanners integrated into data registers use laser beams, from which it follows that the color information for light and dark must relate to the value of the wavelength which is generated by the laser. This means that the gaps in the bar code are "light" for the laser scanning if the gaps have a color which corresponds to the wavelength of the laser. The other regions of the bar code, for example, the bars, then appear "dark" for the laser light. These considerations lead, for example, in the case of glass as a packaging material, to the fact that the glass material as such, which does not reflect, but instead transmits the laser beams at non-printed points, adopts the function of the bars or stripes. The light gaps are then printed onto the glass material in a color which corresponds to the laser light.
For the packaging industry which produces folding cartons, bar codes are generally obtained from printers. For small runs of bar codes, label printers are available which produce bar code labels of paper, metal and plastic and which operate as thermoprinters, matrix printers or laser printers. For measuring and testing the printed bar codes, appropriate measuring and testing instruments are available which also enable color contrast measurements.
For article numbering, the substantially similar EAN and JAN bar codes have become generally accepted world-wide, with the exception of the United States of America. These form the basis of EUROPEAN ARTICLE NUMBERING and JAPANESE ARTICLE NUMBERING, which were designed by the International Article Numbering Association.
A spread of the bar code quality is unavoidable during the production of bar codes by printing, but should be kept as small as possible in order to achieve the clearest possible reading by machines of the bar codes. However, the success of machine reading is not dependent just on the bar code quality, but also on the bar code reader employed, in which, for example, performance fluctuations caused by wear of individual components, such as the laser, the main voltage stabilization unit and the like, can occur. In addition, in practice external influences also act on the bar code, for example, contamination of the packaging material in the region of the bar code, which limits the readability of the bar code.
In printing and reproduction technology, grid scales, exposure test wedges and similar standards, which are constructed similarly to the stripe or bar codes, are used for calibration and quality testing purposes.
Standard, bar and test plates on glass slides are known which comprise zones which are transparent and opaque for polychromatic light, i.e., white light. Lasers, which emit a certain wavelength, are generally not well suited as radiation sources for reading the standard, bar and test plates, since the contrast differences between the glass, which is transparent to white light, and the grating scales and patterns of lines and bars on the plates, which are opaque to white light, are inadequate for the laser light.
In the case of reading and test instruments which work with polychromatic light of a white light source or with monochromatic light of a laser, errors can be caused during the machine identification of bar codes due to performance fluctuations of individual components of the instrument. In addition, specific differences in the machine reading of the bar codes into clear text can occur in the case of instruments from different manufacturers, since each manufacturer tests and adjusts his instruments according to his own bar code models. The test models here can be applied to different materials, such as glass, film, transparent paper, cardboard or the like, which possess thermal, mechanical and optical properties differing from one another. These specific material properties can cause slight deviations during the clear text reading of one and the same bar code by testing instruments and readers of different manufacturers.